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Frequently asked question for developers

Let's collect some questions a lot of Nushell contributors have.

  • How do I do....?
  • Why do I need to do certain things a certain way?

Let's keep the answers concise and up to date (or general enough) to remain relevant

How do I properly test my feature or bugfix?

TODO (Probably fork out into its own file)

I want to report an error to the user

Approximate flow:

  1. Are you reporting the error in the parser/static checking phase?
    • Use nu_protocol::ParseError variants
    • Follow the logic used in the context as we need to collect multiple errors for a good IDE experience
  2. Pick the right nu_protocol::ShellError variant
    • Does a matching existing variant fit your need? (go to references of the ShellError variant for inspiration)
    • Check what context the miette macros add during formatting! (go to definition of ShellError)
    • If it is a one-of specific error, consider using a generic variant
    • Else add a new class of errors
      • add the necessary Span information
      • general shared error text, to inform and point to a resolution
      • dynamic information gathered from the error site
      • Don't use a tuple enum variant, named structs going forward only!
  3. Are you in a command?
    • return Err(ShellError::...) and you're done in a Command::run
  4. Do you want to report a warning but not stop execution?
    • NEVER println!, we can write to stderr if necessary but...
    • good practice: nu_protocol::report_error::report_error or report_error_new
      • depending on whether you have access to a StateWorkingSet
    • if only relevant to in the field debugging: log-crate macros.

Which upstream projects power some of Nu's built-in commands?

A number of Nu's file and system commands are built on uutils/coreutils, a cross-platform Rust reimplementation of the GNU coreutils. These currently include cp, mv, mkdir, mktemp, touch, whoami, and uname (see the uu_* workspace dependencies in the root Cargo.toml). Relying on uutils lets these commands behave consistently across Windows, macOS, and Linux.

How do I check an environment variable?

TODO

WTF is PipelineMetadata?

TODO